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Hydraulic conductivity and microscopic properties of sodium hexametaphosphate-amended sand-sodium-activated calcium bentonite backfill in vertical cutoff walls exposed to lead-contaminated groundwater
This study aims to investigate the hydraulic conductivity of sodium hexametaphosphate (SHMP)-amended sand-sodium-activated calcium bentonite backfill in vertical cutoff walls to contain flow of lead nitrate solutions (Pb(NO3)2), used as simulated lead (Pb)-contaminated groundwater. Workability of SHMP-amended slurry, grain-size distributions and Atterberg limits of SHMP-amended sodium-activated calcium bentonite (conventional bentonite, CB) were evaluated. The results indicated that the SHMP content in slurry was optimized as 2% of the dry weight of bentonite via workability. The SHMP amendment yielded reduced particle diameter and increased clay-sized fraction of the bentonite. When exposed to the simulated Pb-contaminated groundwater, the amended backfill exhibited lower hydraulic conductivity value than 10–9 m/s, while that of unamended backfill increased approximately two orders of magnitude. A series of microscopic tests were conducted to understand why SHMP amendment could improve the chemical compatibility of the backfill. The X-ray diffraction analyses showed an intercalation of SHMP into montmorillonite platelets in the amended backfill permeated with 500 mM Pb(NO3)2 solution. The environmental scanning electron microscopy coupled with energy-dispersive spectrometry analyses indicated that the hydrated amended bentonite along with needle-shaped Pb3(PO4)2 and PbHPO4 were found in amended backfill after permeating with 500 mM Pb(NO3)2 solution in accordance with the X-ray diffraction analysis. The micropore and macropore proportions of amended backfill increased after permeating with 500 mM Pb(NO3)2 solution. The mechanisms of superior hydraulic performance of the amended backfill exposed to lead contamination were attributed to the chemical reaction between lead and SHMP-amended backfill, steric stabilization imposed by the SHMP, and intercalation of SHMP into montmorillonite platelets.
Hydraulic conductivity and microscopic properties of sodium hexametaphosphate-amended sand-sodium-activated calcium bentonite backfill in vertical cutoff walls exposed to lead-contaminated groundwater
This study aims to investigate the hydraulic conductivity of sodium hexametaphosphate (SHMP)-amended sand-sodium-activated calcium bentonite backfill in vertical cutoff walls to contain flow of lead nitrate solutions (Pb(NO3)2), used as simulated lead (Pb)-contaminated groundwater. Workability of SHMP-amended slurry, grain-size distributions and Atterberg limits of SHMP-amended sodium-activated calcium bentonite (conventional bentonite, CB) were evaluated. The results indicated that the SHMP content in slurry was optimized as 2% of the dry weight of bentonite via workability. The SHMP amendment yielded reduced particle diameter and increased clay-sized fraction of the bentonite. When exposed to the simulated Pb-contaminated groundwater, the amended backfill exhibited lower hydraulic conductivity value than 10–9 m/s, while that of unamended backfill increased approximately two orders of magnitude. A series of microscopic tests were conducted to understand why SHMP amendment could improve the chemical compatibility of the backfill. The X-ray diffraction analyses showed an intercalation of SHMP into montmorillonite platelets in the amended backfill permeated with 500 mM Pb(NO3)2 solution. The environmental scanning electron microscopy coupled with energy-dispersive spectrometry analyses indicated that the hydrated amended bentonite along with needle-shaped Pb3(PO4)2 and PbHPO4 were found in amended backfill after permeating with 500 mM Pb(NO3)2 solution in accordance with the X-ray diffraction analysis. The micropore and macropore proportions of amended backfill increased after permeating with 500 mM Pb(NO3)2 solution. The mechanisms of superior hydraulic performance of the amended backfill exposed to lead contamination were attributed to the chemical reaction between lead and SHMP-amended backfill, steric stabilization imposed by the SHMP, and intercalation of SHMP into montmorillonite platelets.
Hydraulic conductivity and microscopic properties of sodium hexametaphosphate-amended sand-sodium-activated calcium bentonite backfill in vertical cutoff walls exposed to lead-contaminated groundwater
Acta Geotech.
Jiang, Zhe-Yuan (author) / Zhang, Run (author) / Li, Zhong-Yuan (author) / Fu, Xian-Lei (author) / Yang, Yu-Ling (author) / Jiang, Ning-Jun (author) / Du, Yan-Jun (author)
Acta Geotechnica ; 20 ; 1235-1250
2025-03-01
16 pages
Article (Journal)
Electronic Resource
English
Conventional bentonite , Hydraulic conductivity , Lead contamination , Microscopic Property , Sodium hexametaphosphate (SHMP) , Workability Chemical Sciences , Physical Chemistry (incl. Structural) , Engineering , Geoengineering, Foundations, Hydraulics , Solid Mechanics , Geotechnical Engineering & Applied Earth Sciences , Soil Science & Conservation , Soft and Granular Matter, Complex Fluids and Microfluidics
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